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ROBUST TRANSMIT PRECODING AND V-BLAST RECEIVER DESIGN
FOR MIMO COMMUNICATION SYSTEMS
by
Jiansong Chen
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(ELECTRICAL ENGINEERING)
December 2008
Copyright 2008 Jiansong Chen

Imperfect channel estimation and unbalanced channel conditions hurdle the realization of the potential high channel capacity of multiple-input-multiple-output (MIMO) systems in real world applications. This thesis research aims at exploring robustness in transmitter precoding and receiver decoding designs to combat these MIMO channel imperfections.; First, we study robust V-BLAST receiver design in point-to-point MIMO links under imperfect channel state information (CSI). Both random and deterministic channel estimation errors are exploited in the study. Given a complex Gaussian CSI estimation error with zero mean and known second-order statistics, we develop two robust symbol detection ordering criteria that optimize the average performance in terms of signal-to-interference plus noise ratio (SINR) and the mean square error (MSE), respectively. When the channel estimation errors are deterministic, unknown yet norm-bounded, a robust ZF nulling operator is derived for ZF V-BLAST receiver to minimize the CSI estimation error power in the worst case. New ordering criteria for symbol detection in each layer are also presented to optimize the worst-case post-detection SINR/MSE.; Next, we extend the robust V-BLAST receiver design to MIMO relay networks under the assumption that random channel estimation errors are independent complex Gaussian with zero mean and known second-order statistics. In this context, ZF relaying at relay nodes and the minimum mean-squared error (MMSE) V-BLAST receiver at the destination terminal are utilized. We derive a robust MMSE nulling operator for the MMSE V-BLAST receiver and develop the corresponding symbol detection ordering criterion at the destination terminal.; Finally, we investigate the problem of robust precoder design in MIMO broadcast channels, since ill-conditioning is intrinsic to a larger user MIMO system. We study the diagonal loading regularization problem for channel inversion by optimizing MSE for each given channel realization with precoding. To compensate the performance loss in multiple access interference (MAI) cancellation by the diagonal loading regularization, we further develop a new channel inversion regularization scheme by applying the generalized Tikhonov method, which turns out to have a generalized loading structure and, thereby, provides better resistance to unbalanced channel conditions (i.e., the near-far effect). We also study a new yet simple power allocation method for precoding schemes based on different channel inversion regularizations.

ROBUST TRANSMIT PRECODING AND V-BLAST RECEIVER DESIGN
FOR MIMO COMMUNICATION SYSTEMS
by
Jiansong Chen
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(ELECTRICAL ENGINEERING)
December 2008
Copyright 2008 Jiansong Chen